How do you approach moving up/down limits?

[Ixnert]

This might more appropriately be in the Psychology forum, but the thrust of my question is mainly as pertains to STTs, and this is where I mostly post/read, so I figured it was better here.

How do you determine when to move up/down limits? Just a question of having enough buyins to feel comfortable? Where you can maximize your hourly earn? Where you can learn the most? Something else?

I'm looking at this in this context: I was beating the 20s very convincingly (25%+ in 300ish -- probably not sustainable but made it clear I was very likely a winning player at that limit) and moved up to the 30s. After a very nice run-up early on, I'm barely positive (~3% ROI) in the last 300.

Considerations of short-term hourly rate say that perhaps I should move back to the 20s, and that would also help my confidence -- winning is nice. But I clearly have more to learn from the 30s than from the 20s, and since my long-term goals include moving up in limits, I clearly need to learn to beat the 30s at some point, as discouraging as it can get at times to not seem to be making any progress.

So those of you that have stepped up through the limits -- what did you do when you get stuck in a rut?